Plate heat exchanger with connection pipes lined with bellows

ABSTRACT

In a plate heat exchanger (1) comprising a package (3) of heat transfer plates (2) arranged between two frame plates at least one of the frame plates (6) is provided with connection pipes (9) for one or two heat exchange fluids. The connection pipes (9) are provided with internal linings (10), which are permanently connected round the ports (4) to an outer heat transfer plate (14) of the package (3) of heat transfer plates (2). Each lining (10) is arranged with room (12) for radial movement inside its connection pipe (9) and provided with at least one bellows (11) adapted--upon relative displacement between the one frame plate (6) and the outer heat transfer plate (14) in a direction across the connection pipe (9)--to facilitate bending of the lining (10). Thereby, a very compact plate heat exchanger (1) can be obtained.

FIELD OF THE INVENTION

The present invention concerns a plate heat exchanger comprising tworelatively thick frame plates between which a package of permanentlyjoined, relatively thin heat transfer plates is arranged. The heattransfer plates may be joined e. g. by welding, brazing or gluing. Theheat transfer plates are provided with inlet and outlet ports, whichform channels through the package for at least one heat exchange fluid.These channels communicate with flow passages, which are formed in theinterspaces between the heat exchange plates. At least one of the frameplates is provided with through holes, which communicate with saidchannels and with the interior of connection pipes firmly connected withthe frame plate. The flow passages between the heat transfer plates, thechannels through the plate package, the through holes in the frame plateand the interior of the connection pipes form the system of flow pathsmaking the flow of heat exchange fluid through the plate heat exchangerpossible.

BACKGROUND OF THE INVENTION

In plate heat exchangers of the kind described above the heat transferplates are often made of stainless steel, whereas the frame plates andthe connection pipes for cost reasons are made of steel which is notstainless. For protection of a frame plate provided with holes and alsoconnection pipes connected therewith from contact with a heat exchangefluid linings, which are preferably made of the same material as theheat transfer plates, are often arranged in the through holes of theframe plate and in the connection pipes. The linings have permanentconnections with the outer heat transfer plate situated closest to theframe plate, around inlet and outlet ports thereof.

The above described lining arrangement in a plate heat exchanger leadsto certain strength problems. The heat transfer plates and the liningsare thin and intended to get into direct contact with the heat exchangefluids, which leads to the consequence that these parts of the plateheat exchanger will quickly adopt the temperature of the heat exchangefluids and, thereby, undergo quick changes in length. The frame plates,on the other hand, are considerably thicker than the heat transferplates and the linings and do not get into direct contact with the heatexchange fluids. Thus, a frame plate with one of its sides is in contactwith an outer heat transfer plate in said plate package and with itsother side is in contact with ambient air. This makes the frame platesundergo a smaller and, above all, slower change in length than the heattransfer plates.

The different changes in length of the heat transfer plates and theframe plates make the linings, their connections with an outer heattransfer plate and the portions of the outer heat transfer plate, whichsurround the ports, to be subjected to large forces which can lead tomaterial breakage with subsequent leakage in the heat exchanger. Theforces will be extremely large if the heat transfer plates and thelinings are made of austenitic stainless steel, which has a particularlylarge coefficient of linear expansion compared to steel which is notstainless and from which the frame plates are normally made.

One solution to the above described problem with material breakage in orat the linings in a plate heat exchanger of the above described kind ispresented in WO 95/31687 A1. This known plate heat exchanger hasconnection pipes 10, which on their insides are provided with linings11. The linings 11, which have permanent connections with the heattransfer plate 3 situated closest to a frame plate 6, are arranged inthe connection pipes 10 with a gap between a respective lining 11 and aconnection pipe. The connection pipes 10 and the linings 11 preferablyhave a length which is at least twice the diameter of the connectionpipes. The length of the linings and said gaps give the linings apossibility of radial movement in their respective connection pipes.Thereby, the forces acting on the linings, on said permanent connectionsand on the outer heat transfer plate are reduced.

A general advantage of plate heat exchangers is their compactconstruction. However, the plate heat exchanger described in the abovementioned WO 95/31687 A1 has a drawback in this respect. Thus, accordingto WO 95/31687, the length of said connection pipes should be relativelylarge , e. g. twice the diameter of the connection pipes, for thelinings to be able to move radially to a desired extent. In practice,even longer connection pipes are used; for instance a plate heatexchanger having heat transfer plates measuring 1750×750 mm and portholes with a diameter of 200 mm may be provided with connection pipeshaving a length of 800 mm. These rather long connection pipes make theplate heat exchanger less compact than normally desired. Moreover, ithas proved that material failure sometimes come up also in plate heatexchangers designed in this way, in most cases round the ports of theouter heat transfer plate.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a plate heat exchangerhaving linings in the connection pipes and being more compact than theplate heat exchanger known previously through WO 95/31687 A1. The basisfor the invention is a plate heat exchanger of the initially definedkind, in which each lining has a permanent connection with an outer heattransfer plate and is arranged with room for radial movement within itsconnection pipe and within the through hole of the frame plate. Theinvention is primarily characterized in that each lining is providedwith at least one bellows adapted--upon relative displacement betweensaid one frame plate and said outer heat transfer plate in a directionacross the connection pipe--to facilitate bending of the lining.Thereby, the stresses acting on the lining, on the permanent connectionand on the outer heat transfer plate in its portion closest to theconnection are reduced.

By the invention each connection pipe may be made very short,consideration having to be made only to the circumstance that saidbellows must have sufficient axial length to allow a desired radialmovement of the lining without it being subjected to unacceptably largeforces. Thereby, a plate heat exchanger according to the invention canbe made more compact than a plate heat exchanger according to theWO-document mentioned above. Thus, a plate heat exchanger of a size asexemplified above may be provided with connection pipes being about halfa meter shorter than earlier.

In plate heat exchangers according to said WO-document material breakagehas sometimes occurred when the plate heat exchangers have been used inapplications where the flow of at least one of the heat exchange fluidsis intermittent. Such a flow results in temperature changes which leadto varying loads on the linings, their said permanent connections andthe portions round the ports of the outer heat transfer plate. Suchvarying loads may give rise to fatigue and fatigue breakdown. A plateheat exchanger, in which the linings have been provided with bellowsaccording to the present invention, can be exposed to temperaturechanges tenfold those to which a plate heat exchanger having liningswithout bellows can be exposed. This gives most likely a margin for thenumber of temperature changes before a fatigue breakdown happens, whichmargin is so large that material breakage in plate heat exchangersaccording to the invention can be avoided completely.

If a plate heat exchanger having linings provided with bellows accordingto the invention is used in applications, in which it is not subjectedto frequent temperature changes, the temperature interval, within whichthe plate heat exchanger can be used, can be made larger than for aplate heat exchanger having linings which are not provided with bellows.

According to a preferred embodiment of the invention the lining has twobellows, one at each end of the lining, a piece of bellows-free liningbeing located between the bellows. A plate heat exchanger provided withlinings according to this embodiment, even though the linings have twobellows, can be made more compact than a plate heat exchanger havinglinings without any bellows. An arrangement of two bellows makes eachone of the bellows being exposed to less bending than a sole bellowsand, accordingly, the risk of fatigue breakdown is even smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described more closely in the following withreferences to the accompanying drawings, which in FIG. 1 and FIG. 2 showtwo embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a section through a part of a permanently joined plate heatexchanger 1 according to a first embodiment of the invention. A numberof rectangular heat transfer plates 2 are permanently joined with eachother, for example through welding, forming a plate package 3. Each heattransfer plate 2 is provided with four ports 4, one in each corner ofthe heat transfer plate 2. The ports 4 of the heat transfer plates 2form four channels for two heat exchange fluids through the platepackage 3. In FIG. 1 only two channels 5a, 5b are shown, forming aninlet for one of the heat exchange fluids and an outlet for the otherheat exchange fluid, respectively. The plate package 3 is mountedbetween two frame plates, of which only one frame plate 6 is shown inFIG. 1. The two frame plates are held together by a number of bolts 7.

The frame plate 6 is provided with through holes 8 aligned withrespective channels 5a, 5b. At the through holes 8 connection pipes 9are firmly connected to the frame plate 6. By means of the connectionpipes 9 the plate heat exchanger 1 can be connected to conduits, throughwhich the two heat exchange fluids shall flow to and from the plate heatexchanger 1, respectively. The connection pipes 9 on their insides areprovided with linings 10, and each lining 10 is provided with a bellows11. Between each connection pipe 9 and its lining 10 there is a gap 12.Each lining 10 at one of its ends, by means of a connection 13, ispermanently connected to an outer heat transfer plate 14 around one ofits ports 4. An intermediate ring 15 can be a part of the connection 13to facilitate the joining of the lining 10 with the outer heat transferplate 14. At its other end the lining 10 is formed so that it can beclamped between a flange 16 on the connection pipe 9 and a flange (notshown) on one of the above mentioned conduits. In FIG. 1 only two out offour connection pipes and linings are shown.

Between the heat transfer plates 2 flow passages 17 are formed for thetwo heat exchange fluids. Every second such flow passage communicateswith the inlet channel 5a for one fluid but is closed from communicationwith the outlet channel 5b for the other fluid. These flow passages alsocommunicate with an outlet channel (not shown) similar to the inletchannel 5a. The remaining flow passages are closed from communicationwith the inlet channel 5a but communicate with an inlet channel (notshown) for the other fluid and with the outlet channel 5b.

When the plate heat exchanger 1 is in operation, a temperaturedifference often arises between the plate package 3 and the frame plate6, causing that the plate package 3 and the frame plate 6 undergodifferent changes in length. If, for example, the outer heat transferplate 14 is subjected to an extension larger than that of the frameplate 6, the permanent connection 13 of the linings 10 will be displacedrelative to the connection pipe 9. The connection 13 and the lining 10then are radially displaced inside one end portion of the connectionpipe 9, since the gap 12 permits this. At the other end portion of theconnection pipe 9, i. e. in the area of the flange 16, the lining 10remains substantially immovable relative to the connection pipe 9.

Upon radial displacement of one end of the lining 10, the lining 10 willbe bent and, thus, some portions of the lining 10 will be extended andothers shortened. The bellows 11 is adapted to absorb these extensionsand shortenings and, thereby, reduce stresses acting on the lining 10,the permanent connection 13 and the outer heat transfer plate 14 in itsportion closest to the connection 13.

A preferred second embodiment of a lining intended for a plate heatexchanger according to the invention is shown in FIG. 2. For similardetails in FIG. 1 and FIG. 2 the same reference numbers have been used.

The plate heat exchanger 1 in FIG. 2 is of the same kind as the onedescribed above but differs in respect of the design of the lining 10.As can be seen, each lining 10 is provided with two bellows 18, 19; onebellows at each end of the lining 10. Each separate bellows 18, 19 willbe subjected to less bending than the single bellows 11 in theembodiment according to FIG. 1.

Each one of the bellows 11 and 18, 19, respectively, should have asufficient number of folds to fulfil its purpose. In a lining providedwith only one bellows 10-12 folds can be adequate for the bellows. In alining provided with two bellows each bellows preferably has 5 folds.

The folds of the bellows are preferably not sharp but rounded, e. g.shaped as adjoining semi circles.

A bellows of the above described kind, particularly in a lining providedwith only one bellows, advantageously may be formed as a multilayeredbellows, i. e. the bellows may comprise several thin sheet metal layers.

What is claimed is:
 1. A plate heat exchanger (1) comprising:a package(3) of heat transfer plates (2) provided with inlet and outlet ports(4), said ports forming channels through the package (3) for at leastone heat exchange fluid, two frame plates (6) between which said package(3) of heat transfer plates (2) is mounted such that an outer heattransfer plate (14) of the package (3) is situated adjacent to one ofthe frame plates (6), at least said one frame plate (6) having at leastone through hole (8), which communicates with one of said channels, atleast one connection pipe (9) firmly connected with said one frame plate(6) around its through hole (8), and at least one tubular lining (10),which by means of a permanent connection (13) is connected to said outerheat transfer plate (14) around one of said ports (4) and which extendsthrough said through hole (8) and said connection pipe (9), the lining(10) being arranged with room (12) for radial movement in the connectionpipe (9), wherein said lining (10) is provided with at least one bellows(11) having folds adapted--upon relative displacement between said oneframe plate (6) and said outer heat transfer plate (14) in a directionacross the connection pipe (9)--to facilitate bending of the lining. 2.The plate heat exchanger (1) according to claim 1, wherein said lining(10) is provided with two bellows (18, 19) arranged one at each end ofthe lining (10) and with a piece of bellows-free lining located betweenthe bellows (18, 19).
 3. The plate heat exchanger (1) according to claim1, wherein said permanent connection (13) between said lining (10) andsaid outer heat transfer plate (14) comprises an intermediate ring (15).4. The plate heat exchanger (1) according to claim 1, wherein the foldsof said bellows (11 or 18, 19) are rounded.
 5. The plate heat exchanger(1) according to claim 1, wherein each bellows (11, 18, 19) is amultilayered bellows comprising several thin sheet metal layers.
 6. Theplate heat exchanger (1) according to claim 2, wherein said permanentconnection (13) between said lining (10) and said outer heat transferplate (14) comprises an intermediate ring (15).
 7. The plate heatexchanger (1) according to claim 2, wherein the folds of said bellows(11 or 18, 19) are rounded.
 8. The plate heat exchanger (1) according toclaim 3, wherein the folds of said bellows (11 or 18, 19) are rounded.9. The plate heat exchanger (1) according to claim 2, wherein eachbellows (11, 18, 19) is a multilayered bellows comprising several thinsheet metal layers.
 10. The plate heat exchanger according to claim 3,wherein each bellows (11, 18, 19) is a multilayered bellows comprisingseveral thin sheet metal layers.
 11. The plate heat exchanger accordingto claim 4, wherein each bellows (11, 18, 19) is a multilayered bellowscomprising several thin sheet metal layers.